The present invention relates to power sources, and more particularly to DC-DC regulators.
DC-DC regulators are well known in the art. FIG. 1. illustrates a conventional DC-DC regulator. The conventional DC-DC regulator 100 is a variable frequency resonant DC-DC regulator. The regulator 100 comprises a pull-pull driver 102 with a Voltage Controlled Oscillator (VCO) 124, a zero-current switch 104 (ZCS) with switching transistors 126 and 128, a resonant circuit 130 with transformer 106 (TI) and a capacitor 108 (C2), a synchronous rectifier 132, a sensing circuit 134 with resistors 112 and 114 and an error amplifier 116, and an opto-coupler 118 with a diode 120 and a transistor 122.
The DC output voltage is sensed by R1112 and R2114 and fed to the error amplifier 116. The error amplifier 116 compared the DC output voltage against VREF. The output of the error amplifier 116 drives a current proportional to the error voltage through the opto-coupler diode 120 of the opto-coupler 118, which then develops a voltage across the transistor 122 of the opto-coupler 118. This variable voltage so developed is applied to the VCO 124 which changes the frequency of the push-pull driver 102.
To maintain a constant DC output voltage, the conventional DC-DC regulator 100 changes the frequency of the push-pull driver 102 to maintain zero current switching (ZCS) operation. However, this prevents the push-pull transistors of the ZCS from operating in ZCS mode over the full range of operations. This may result in the loss of zero-current switching, high dissipation in the regulator, and unpredictable behavior due the wide range of frequencies.
Accordingly, there exists a need for an improved DC-DC regulator. The improved DC-DC regulator should maintain a substantially constant DC output voltage without changing the frequency of the oscillator. The present invention addresses such a need.
A multiphase zero-volt switching (ZVS) resonant DC-DC regulator includes: a zero-volt switch (ZVS); a DC output voltage means; a variable resonant circuit; a synchronous rectifier; and a sensing circuit. The sensing circuit senses a DC output voltage at the DC output of the regulator. The regulator uses the resonant circuit in conjunction with the sensing circuit to provide a substantially constant DC output voltage at a fixed frequency. If the sensing circuit senses a change in the DC output voltage, then a resonant frequency of the regulator is changed by the variable resonant circuit. This allows the oscillator of the regulator to maintain a fixed frequency, thus ensuring the availability of zero-volt switching over the full range of operation. The regulator also has the advantages of low power loss, reduced ripple, and a very fast transient response time.